What's up on the roof?

There has never been a better time for the application of commercial packaged rooftop systems. The strong U.S. economy is one reason. New construction in the commercial marketplace has increased steadily over the past few years, supporting a healthy growth pattern for rooftop air conditioning units.

Figure 1 (on page 34) shows the number of rooftops installed domestically over the past three years. In 1998 and 1999 alone, overall usage of packaged systems increased at a rate of 12% and 10%, respectively. Larger packaged systems, which are composed predominantly of rooftops, grew at an even higher rate of about 20% in 1998 and 1999 (source: ARI, 1999).

Some key underlying trends have driven growth of rooftops, and suggest that these units will remain a growth area over the next several years. National chain store development, changing U.S. population demographics, higher air quality standards, and new trends in system design have all contributed to a larger number of rooftop units installed at commercial locations everywhere.

Chain stores on the rise

The 90s witnessed strong growth of national chain stores. Franchises as varied as Wal-Mart, CVS Pharmacies, Home Depot, Auto-Zone, McDonalds, and Out-back Steak House all enjoyed exceptional growth.

Most of these stores have similar national designs, and in many cases have centralized their hvac equipment designs to make sure uniform standards are kept. A store in Portland, OR looks the same as a store in Atlanta, GA, for example.

These buildings tend to be one story tall, with high ceilings and spacious interiors, making them ideal for multizone solutions that today’s rooftop units provide.

Other building types that have seen high growth in the 90s fall in the mid-size range, including hotels-motels, schools, small suburban offices, and professional buildings.

Demographics and IAQ

Also fueling this growth has been the continued population shift and growth in the Southeast and Southwest, where land is still relatively inexpensive and available. Cities like Las Vegas NV, Dallas TX, and Phoenix AZ have all seen very high growth rates.

Demographic studies support this growth and most project continued high population growth for the foreseeable future.

Increased compliance of indoor air quality (IAQ) standards, sometimes prompted by increasing legal pressure, is the force behind strong growth in replacement systems. One reason for the decline in water-cooled systems below 300 tons is concern over mold spores, which frequently occur with such systems.

More and more building owners are opting for air-cooled designs when they need to replace units.

Figure 1. Rooftop units installed domestically over the past three years.

A changing marketplace

Today’s rooftop units are more compact and have been designed to be able to accommodate many of the older building designs. Many contractors are replacing older central units with multiple, smaller packaged rooftops.

Public buildings like schools, hospitals and other medical facilities, government offices, and nursing homes have all been forced to make these changes to comply. This trend shows no sign of abating.

Finally, the move to rotating technology has given air conditioning equipment designers a new range of compressors from which to choose. Screw designs are available today for large air conditioning systems. New, higher efficiency scroll designs have also been introduced to the market, and are available for 5- to 120-ton applications.

Scroll compressors in particular have allowed designers the flexibility to develop the smaller, lightweight systems that have fueled much of the commercial rooftop growth. They also increase design flexibility by allowing more redundancy in systems.

Many of today’s rooftops have three to eight refrigeration circuits instead of the more traditional configuration of two. Rather than the entire system going down, the loss of a circuit does not impact a store as much. Indeed, many new store designs size their hvac loads with excess capacity so the loss of one circuit has minimal impact.

Service calls become routine, not expensive emergencies. This is especially important in an era where labor costs are increasing.

In the future

Other key trends on the horizon will impact the commercial rooftop market.

First, the long-discussed ASHRAE 90.1 Standards will go into force in late October 2001. These standards will require system redesigns that boost the EER of rooftops anywhere from 10% to 15%, creating energy savings and a better value for store owners.

At the same time, the continued transition to HFC refrigerants will also impact system designers over the next two to five years. Current testing supports a trend to R-410A in packaged rooftop units, as several manufacturers are already planning R-410A test sites.

This refrigerant alternative is leading in the rooftop market because it offers better efficiency levels than the other HFC contenders, R-134a and R-407C.
R-410A should also provide better system reliability with its inherent lower refrigerant charge requirements.

System manufacturers aren’t the only ones who will feel the impact of these impending new standards and regulations. The industry’s service technicians will face changes as virtually every rooftop unit on the market will be redesigned to meet the new efficiency standards and for HFC refrigerant compatibility.

In response to these changes, compressor manufacturers are focusing their development efforts on new and better products for the commercial rooftop market. In the next few years, expect to find new, larger horsepower scroll designs suitable for R-410A and new screw compressors for larger rooftop systems.

In summary, the recent surge in rooftop units can be attributed to a combination of trends: a strong economy, the U.S. population shift, the growing number of national chain stores, and a trend toward more efficient and compact systems made possible by rotating compressor designs.

The path to the future is not without challenges, but the industry as a whole will benefit from better, more reliable rooftops, greater energy savings, and cleaner air.

Publication date: 08/21/2000

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